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...Algorithm: this is probably the most contentious area. Every computer is made with at least one (some have 2 that can be switched). Some are quite aggressive (will give longish NDL while getting you out of the water fairly quickly) whereas others are more conservative (will give a larger margin of safety). All computers will allow a range of conservatism to allow you to tailor it depending on fitness etc. Read up on the algorithm(s) for the computer you are looking at before you buy it...

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Good advice. Below is a relatively complete listing of available computer brands and the decompression algorithms they run. I have categorized each as conservative, moderate, or liberal. Feel free to disagree with my categories, mainly based on 1st dive NDLs and ScubaLab hyperbaric unit repetitive dive simulations. The emphasis here is no stop diving. The availability of hoseless air integration is designated.
Dive computer brands and decompression algorithms

Hello. Just got my ow certification. Looking to buy my first dive computer. Could someone explain what is usually the difference between a beginner dive computer and a mid ranged computer? More specifically, I wanted to know till what point can i use a beginner/budget computer before I need to upgrade. Can I safely use one till the 40m limit? Thanks

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Today, a beginner dive computer can be safely used well beyond beginner range. If you start getting into the tech range, and doing deco dives, then you may want to look into a more tech oriented computer, but until then your recreational computer will work just fine.

Years ago, you used to be able to buy an air only computer. Haven't seen one of those in years. May still exist, just haven't seen any. All the computers I see out there are at least Nitrox capable. Comparing an entry level and higher end computer from the same company, you'll find that the same algorithm is most likely used. The higher end computer may offer things like air integration, and a nicer screen, but they'll most likely calculate your dive the same.

There are, however a few things I'd consider when looking at a beginner dive computer. First, is buttons. The more buttons, the better. I won't touch a single button computer. Too hard to navigate. Two buttons is better, three or more is best. Next, take a look at navigating the menus. Some are intuitive, others are not. Third, make sure that batteries are user replaceable and readily available.

I went with a Suunto Zoop Novo. Basic functionality to recreational depths and nitrox compatibility to 40% seemed to be table stakes for dive computers, but I liked that the Zoop Novo has a depth alarm and elapsed dive time, has a user changeable battery, and has 4 buttons. Also has a decent sized screen for the price point. I recently made a video about it:

The way I narrowed down the decision was by looking at the natural stratifications of models -- you have some really simple one button models at one price point, then another ~$100 gets you more buttons (e.g. easier use) and more features like alarms, better screen, logging and downloads. After that you're spending a whack more to get compass and/or air integration, color display, multi gas, etc, so by sticking in that second tier I was able to narrow it down and not spend more than I needed at this stage in my diving.

I figure if I get advanced enough that I need a more awesome computer on my wrist that this will make a good backup.

I just went through this myself. I basically did what you are doing, asking people their opinions, and Googling reviews. I probably changed my mind three times. Talk to your dive shop about what they recommend, and then look at what other people suggest. What I found earlier this year were the same basic 'beginner' dive computers, so you start to figure out features that you want/need and don't need.

I ended up with a Mares Matrix because it had the features I wanted, but also the display and four buttons were more in line with what I liked using and seeing.

More specifically, I wanted to know till what point can i use a beginner/budget computer before I need to upgrade.

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I expect most common reasons to upgrade are
- I want a new toy,
- I bought my own regs and want to add a wireless air pressure sensor,
- I am going into decompression training and need a computer designed for decompression diving.

I expect most common reasons to upgrade are
- I want a new toy,
- I bought my own regs and want to add a wireless air pressure sensor, - I am going into decompression training and need a computer designed for decompression diving.

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Even the Suunto Zoop is full decompression dive computer. The last time I saw a computer that didn't give you decompression information was back in the 90's --- An Aladin Black. It just said STOP and a depth. Crazy.

I expect most common reasons to upgrade are
- I want a new toy,
- I bought my own regs and want to add a wireless air pressure sensor,
- I am going into decompression training and need a computer designed for decompression diving.

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And, I bought a computer with a conservative deco algorithm and wish I had one with a more liberal decompression algorithm.